Radar tomography

ABSTRACT

A radar tomography method and apparatus generates a plurality of radar pulses in a transmitter and projects them with an antenna toward a patient. Radar pulses reflected from the patient are picked up by the antenna and conducted to a receiver. Predetermined radar pulses are selected from among the received pulses by a timer/gate circuit connected to the receiver. The selected radar pulses correspond to a predetermined area of interest within the patient. A representation of the predetermined area within the patient may be displayed with known display apparatus. The antenna may also be moved relative to the patient, in order to produce three-dimensional information. Synchronizing the transmitter, the time/gate device, and the movement of the antenna may be effected with a synch processor, and a matrix filter may be used to focus the emitted radar pulses and to reduce noise in the return radar pulses.

BACKGROUND OF THE INVENTION

The present invention relates to medical imaging apparatus and method,and particularly to tomography utilizing radar pulses.

A variety of medical imaging modalities are known and include nuclearmagnetic resonance, ultra-sound, sonography, positron emission, digitalsubtraction angiography, and x-rays. Computed tomography is a well-knownmethod for manipulating data to produce medical images. For example,ultra-sound, positron emission, and X-rays may utilize computedtomography techniques to produce images for diagnosis. A recent article,"III Imaging With Photons", by Edward Rubenstein, appearing in theDecember, 1988, edition of CURRENT TRENDS IN MEDICINE, explains severalof these imaging methods and is incorporated herein by reference.

However, all known medical imaging modalities are considered to beeither too expensive or may be at least somewhat harmful to the patient.For example, a nuclear magnetic resonance machine may cost $2.5 millionand require almost one-thousand dollars to produce an image. On theother hand, the use of X-rays is disadvantageous in that repeated usemay result in harm to the patient.

Furthermore, known imaging techniques can create an image by passingenergy through the patient to produce a projected image or across-sectional image of the patient. The power required to pass certaintypes of energy and energized particles through a patient is expensiveto produce and may cause harm to patient tissue.

Thus, the medical practitioner often is presented with the dilemma ofchoosing between the desire to perform a thorough diagnosis andexcessive cost or patient harm resulting from such thorough diagnosis.In fact, medical insurance companies are demanding greater use ofmedical imaging equipment, while patients are being informed by themedia and various consumer advocates that increased use of, for example,X-rays is unnecessary and harmful. Therefore, medical personnel areplaced in the difficult position of trying to satisfy both theirpatient's needs and their insurer's requirements.

Accordingly, what is needed is a simple, fast, low-cost medical imagingtechnique which causes no harm to the patient.

It is known that radio waves will penetrate human tissue, and that radiowavelengths of electromagnetic radiation are considered non-ionizing,thus causing no radiation damage. For example, current technologiesemploy short-wave and microwave radiation to treat deep muscle injurywith controlled heat. No tissue damage occurs even when the radio wavesare applied steadily for periods of up to 30 minutes. U.S. Food and DrugAdministration (FDA) guidelines for use of such modalities are currentlyavailable. Furthermore, radar technology is relatively well developed inmilitary and civilian aviation. In addition, the proliferation of radarguns and related equipment in traffic enforcement is well-known.

Radar uses a wavelength of several meters to several millimeters. Radarcan also be focused into more concentrated beams than X-rays. Inaddition, sensitive radar receivers are available which can image anobject at great distances registering a small fraction of the radiatedenergy. Radar also produces an image by reflecting energy from anobject, thus requiring less power and producing less tissue damage inthe patient than known techniques. Thus, it appears that radar signalsmay be useful in medical imaging.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a medical imagingmethod and apparatus utilizing radar signals

In order to achieve the above object, the present invention is directedto a method and apparatus for emitting a plurality of radar or radiopulses toward a subject with an antenna, providing the radar pulses tothe antenna with a transmitter, and receiving the plurality of radarpulses reflected from the subject with a receiver. A timer/gate circuitis used to select predetermined radar pulses from among the received,reflected radar pulses. The radio pulses selected are those whichcorrespond to a predetermined area, at a predetermined depth, ofinterest within the subject.

Preferably, the timer/gate circuit can be controlled in order to scanthe predetermined area throughout the subject.

If desired, a three-dimensional image of a predetermined volume withinthe subject can be produced by generating relative movement between theantenna and the subject. This produces a sequence of scans at differingdepths within the target volume within the patient. A processor thenstores and manipulates the view data in order to produce athree-dimensional view of the predetermined volume within the subject.

In order to more accurately focus the emitted and reflected radarpulses, the present invention may include a matrix filter, coupled tothe antenna, which reduces noise by eliminating unwanted reflection anddiffraction components. The matrix filter may include a plurality ofradar absorbing tubes disposed to form a grid in cross-section.

Of course, the present invention may also include display means fordisplaying the predetermined two and three-dimensional areas within thesubject.

The advantageous structure and functions according to the presentinvention will become readily apparent to those of ordinary skill inthis art from the following detailed description of the preferredembodiment, taken together with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic block diagram of the apparatus according to thepreferred embodiment; and

FIG. 2 is a perspective view showing the matrix filter of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The principle of radar is relatively simple. Radio wave energy isemitted toward an object and its position and relative movement may bedetermined through the return radio echo. The frequency of the radiopulses and the intensity of each pulse may be varied in accordance withthe type of echo desired, the relative distance to and movement of thesubject, and the type of antenna used. From the return echo, thedistance to the object may be readily calculated by well-known Dopplertechniques. The signal-to-noise (SNR) ratio of the return echo pulsesmay be diminished by resonance, diffraction, or off-phase interference.Techniques for reducing resonance (artificial wave amplification), andoff-phase interference are well-known and could be implemented in thepresent invention.

Diffraction may reduce the SNR by causing scattering of the returnpulses into the receiver. As will be discussed below, the presentinvention proposes a matrix filter in order to reduce diffraction noise.

Producing a medical image from the return echo pulses can be a matter ofapplying existing technology. Well-known computed tomography techniquesmay be used to process the return radar signals in order to produceusable images for medical diagnosis. For example, a timer/gate devicemay be used to gate the receiver so that it receives only pulses from aselected distance. Another technique is to utilize a so-called rangefilter in which a plurality of range bins are disposed. A return radarsignal entering a particular range bin indicates that the subject is ata predetermined distance from the antenna. Such techniques are known inthe radar field and need not be described in greater detail herein.

Referring now more particularly to the drawing, FIG. 1 is a blockdiagram of a preferred embodiment of the present invention. Thisembodiment is a radar tomography device adapted for use in dentistry toexamine a patent's teeth, although the principles of the presentinvention may be adapted to a wide variety of medical imagingapplications and devices.

In FIG. 1, the patient or subject 2 is exposed to pulsed radio signals 4emitted from an antenna head 6. As schematically shown there, antennahead 6 includes an antenna 8, an aperture control device 10, a matrixfilter 12, and a cone or cylinder spacer 14. A standard dental X-raycone is usually 8 or 18 inches long, and therefore, an 18 inch cone orcylinder spacer 14 would be quite normal for use with the patient and bymedical personnel. In addition, an 18 inch spacer 14 would provideapproximately a 1 meter path for rays emitted from the antenna andreflected from the subject.

Antenna 8 may comprise any well-known or conventional radar antenna. Forexample, parabolic, Cassegrain, dipole, or flat semi-conductor antennasmay be used. The antenna should be simple, light-weight, andinexpensive. The antenna should also be small enough to fit into theantenna head 6 and allow for ease of operation by medical personnel.

The aperture control device 10 is used to control the aperture of theantenna 8. This device 10 may include synthetic aperture controlcircuitry, or mechanical means such as two plates of radar-absorbingmaterials with slits moving in opposite directions allowing synchronousradiation emission and reception through one aperture at a time.Additionally, while the aperture control 10 is shown located between theantenna 8 and the filter 12, it may be located between the filter 12 andthe patient 2. Again, such aperture control devices are relativelywell-developed and need not be described in further detail here.

A matrix filter 12, as mentioned earlier, is used to reduce diffractionnoise from the reflected return signal, and to properly focus theemitted signal on the area of the patient of interest. The matrix filter12 may be designed in a predetermined pattern to correspond to thenumber of scans desired, and the location of the area of interest withinthe subject. A detailed description of one preferred embodiment of amatrix filter 12 will be provided below with reference to FIG. 2.

A duplexer 16 is provided to switch the antenna between a transmittingmode and a receiving mode. In the absence of the duplexer, thetransmitted energy may harm a receiver 22 connected therethrough toreceive the reflected radiation. Again, duplexers are very well knownand are readily available. Of course, two antennae (one fortransmitting, one for receiving) may be used in the present invention,thus eliminating the need for a duplexer.

A transmitter 18, also connected to the dupluxer 16, is a high-poweroscillator which generates the radar pulses at a predeterminedfrequency, amplitude, and phase. A modulator 20 provides pulses of inputpower to activate the transmitter 18. For the duration of the inputpulse from the modulator 20, the transmitter 18 generates a high-powerradio frequency wave, converting a DC pulse to a pulse of radiofrequency energy. The exact frequency of the emitted energy may be tunedto any appropriate range, as desired. The generated radio wave pulsesare then transmitted to the antenna 8 through the duplexer 16.

The receiver 22 receives the reflected radar pulses from the antenna 8through the duplexer 16. Typically, the receiver 22 is a superheterodynereceiver which translates the received signals from their frequency to alower, intermediate frequency at which they can be filtered andamplified more conveniently. Translation is usually accomplished byadding the received signals to the output of a low-power localoscillator in a mixer. The output of the mixer is usually amplified andthen filtered to reduce interfering signals, electrical backgroundnoise, resonance, and off-phase interference noise. Finally, theamplified received signals are output to a video processor 26 through atimer/gate 24 discussed below in detail. Radar receivers as describedabove are well known and need not be explained in further detail.

The timer/gate 24 is a device which selects predetermined pulses fromamong the received pulses in order to effect spatial control. Forexample, as the radar pulses are reflected back from the lower jaw ofthe patient 2, the timer/gate 24 selects only those return pulses timedto return from a desired depth (for example, 2 centimeters from theforward edge of radar head 6). Accordingly, only the gated pulses wouldbe accepted for imaging. Preferably, timer/gate 24 controls the receiver22 so that it only receives radar pulses from the desired location. Byvarying the return-plane distance within the patient by moving theantenna head toward or away from the volume of the patient under study,or by varying the time of acceptable pulse return, readings can beobtained for any desired tissue depth within the patent 2. Thetimer/gate 24 must be very sensitive since the patient 2 will bepositioned close to the radar head 6. Timers capable of measuringpicoseconds are now known. For example, such a timer identified by ModelNo. DG-535 is available from Stanford Research.

By moving radar head 6 relative to the patient 2, and then scanning inthe depth direction through operation of the timer/gate 24, informationmay be derived in three-dimensions. Such techniques are well-known inthe computed tomography field. This method will allow volumetricinformation to be obtained from the subject.

The video processor 26 receives the selected output from receiver 22 andprocesses the signal to produce a video signal capable of being storedin a video storage device 28, and/or displayed on video display 30.Apparatus such as the video processor 26, video storage 28, and videodisplay 30, are known and available.

A synch processor 32 synchronizes the operation of the apparatus.Specifically, the transmitter 18 and video processor 26 are synchronizedby generating a continuous stream of very short, evenly spaced pulses.They designate the times at which successive radar pulses are to betransmitted, and are supplied simultaneously to the modulator 20 andvideo processor 26. In addition, synch processor 32 controls timer/gate24 to effect proper scanning control. Such synch processors are widelyused in radar devices, and in computed tomography apparatus, andtherefore, can be readily adapted to the present invention.

A high-resolution image of the area or volume of interest may also beobtained by providing relative movement between the antenna head 6 andsubject 2. Thus, the movement control device 34 may be coupled to theantenna head 6 to move it with respect to patent 2. In a manner similarto a CATSCAN, the antenna head 6 may be moved in an arc around subject 2in order to take several "shots" or "views" of the subject 2. In eachview, the radar pulses are scanned in the X and Y directions by use ofthe aperture control 10, and in the depth direction by using thetimer/gate 24. When information regarding the plurality of "views" iscombined, a higher resolution image of the volume of interest may beobtained. Those having skill in this field will understand that theprinciples of image processing used in a CATSCAN device can be adaptedto the present radar tomography device.

The signal output from the video processor 26 is an analog video signalcapable of being stored on the video storage device 26 (for example, aVCR), or displayed on the video display device 30. However, digitaltechniques offer significant opportunities for image enhancementTherefore, the analog signal from the video processor 26 may be providedto an analog-to-digital converter 36 to digitize the signal. Thedigitized signal is then provided to a digital processor 38 which canmanipulate the data in a variety of well-known ways. For example,information from a plurality of "views", as discussed above, may becombined within the processor 38 to produce a high-resolution,three-color, three-dimensional view of a volume of interest withinsubject 2 Such images may then be converted to an analog signal by adigital-to-analog device 42 for display on the video display 30. Thedigital output from the processor 38 may also be provided to a memory 40which stores the information for later retrieval and use. Imagingprocessors such as those used in nuclear magnetic resonance imaging maybe adapted for use in the present invention.

FIG. 2 is a perspective view of a preferred embodiment of the matrixfilter 12. The matrix filter 12 has the dual function of focusing theemitted radar energy on the area of interest and eliminating diffractionnoise from the reflected return pulses. Diffraction caused by scatteringof the return waves is avoided by the size of the matrix filter 12.Matrix filter 12 is preferably a radar-absorbing 10 centimeter squareparallel filtering box, broken into a cross-sectional grid of squaretubes. The grid comprises a plurality of perpendicularly disposedradar-absorbing panels 121. The number and spacing of the panels may bemodified somewhat, depending upon the desired radar frequency, phase,and power. Alternatively, the filter may be made of a matrix of parallelcylindrical tubes of radar-absorbing materials. Of course, the tubes maybe of other cross-sectional shapes Again, the design of such filters isfairly well developed in the radar field.

Thus, what has been described is a medical imaging modality usingradar-frequency signals to produce inexpensive, high-resolution imagesof a subject. The apparatus utilizes existing technology, and therefore,should be relatively inexpensive to manufacture, market, and operate.Furthermore, medical insurers and patients alike will welcome such asafe, low-cost alternative to X-rays and nuclear magnetic resonance.

The specific structural details of the devices represented by blocks inthe schematic diagram of FIG. 1 are per se well-known or could bereadily constructed by the person of ordinary skill in this fieldwithout undue experimentation. Therefore, the exact structure of theblocks in the schematic is not described in detail in order to moreclearly describe the present invention, and since such details are notcritical to the best mode of carrying out the present invention.

While the present invention has been described with respect to what ispresently considered to be the preferred embodiment, it is to beunderstood that the invention is not limited to the disclosedembodiment. To the contrary, the present invention is intended to covervarious modifications and equivalent arrangements included within thespirit and scope of the appended claims. The scope of the followingclaims is to be accorded the broadest interpretation so as to encompassall such modifications and equivalent structure and functions.

What is claimed is:
 1. A radar tomography apparatus, comprising:antennameans for emitting a plurality of radar pulses toward an adjacentpatient; transmitter means for providing the plurality of radar pulsesto said antenna means; receiver means for receiving a plurality ofreflected radar pulses which correspond to the emitted plurality ofradar pulses reflected from subdermal features within the patient; andtimer/gate means for selecting predetermined radar pulses from among thereceived radar pulses, the selected radar pulses corresponding to apredetermined area of interest within the patient, the selected pulsesincluding pulses which discriminate subdermal structure from contiguoussubdermal structure.
 2. Apparatus according to claim 1, furtherincluding display means for displaying a representation of thepredetermined area within the patient based on the selected radarpulses.
 3. Apparatus according to claim 2, wherein said display meanscomprises:a video processor for converting the selected radar pulsesinto a video signal; and a video display for receiving the video signaland displaying the representation of the predetermined area of thepatient.
 4. Apparatus according to claim 3, further including:ananalog-to-digital circuit for converting the video signal from saidvideo processor into a digital signal; a digital processor for receivingthe digital signal from said analog-to-digital circuit, processing thedigital signal, and providing an output digital signal which correspondsto the predetermined area within the patient; and a digital-to-analogcircuit for converting the output digital signal into an analog signalfor display on said video display.
 5. Apparatus according to claim 4,further comprising memory means for receiving the output digital signalfrom said digital processor, storing the output digital signal, andproviding a plurality of stored digital signals to said digitalprocessor to cause said video display to display a plurality ofpredetermined areas within the predetermined.
 6. Apparatus according toclaim 1, further including a matrix filter, coupled to said antennameans, for directing both the emitted radar pulses and the reflectedradar pulses.
 7. Apparatus according to claim 1, wherein said antennameans comprises:a spacer head; an antenna coupled to said spacer head;an aperture control device for controlling an aperture of said antenna;and a duplexer for switching said antenna between said transmitter meansand said receiver means.
 8. Apparatus according to claim 7, furtherincluding a matrix filter, coupled to said antenna, for directing theemitted radar pulses and the reflected radar pulses.
 9. Apparatusaccording to claim 1, wherein said transmitter means comprises:atransmitter for generating a plurality of generated radar pulses; amodulator for modulating the generated radar pulses to produce theplurality of radar pulses provided to said antenna means; and a synchprocessor for controlling the modulator to produce the plurality ofradar pulses at predetermined timings.
 10. Apparatus according to claim9, further comprising a video processor for converting the selectedradar pulses into a video signal; andwherein said synch processorsynchronizes operation of said modulator and said video processor.
 11. Aradar tomography apparatus comprising:an antenna for emitting aplurality of radar pulses toward an adjacent patient, and for receivinga plurality of reflected radar pulses reflected from subdermal featureswithin the patient; a filter for guiding the emitted and reflectedpulses toward and from the patient, respectively; a transmitter forproviding the plurality of radar pulses to said antenna; a receiver forreceiving the plurality of reflected radar pulses from said antenna; atimer/gate circuit for selecting predetermined ones of the reflectedradar pulses received by said receiver, the selected radar pulsescorresponding to a predetermined area of interest within the patient,the selected pulses including pulses which discriminate subdermalstructure from contiguous subdermal structure; and display circuitry forreceiving the selected radar pulses from said timer/gate circuit anddisplaying a representation of the predetermined area within thepatient.
 12. Apparatus according to claim 11, further comprising anaperture control device for controlling an aperture of said antenna. 13.Apparatus according to claim 12, further comprising a synch processorfor synchronizing operation of said aperture control device, saidtransmitter, said timer/gate circuit, and said display circuitry. 14.Apparatus according to claim 11, wherein said filter comprises abox-like structure having a plurality of radar-absorbing panels disposedmutually perpendicularly therein.
 15. Apparatus according to claim 11,wherein said display circuitry comprises:a video processor for receivingthe selected radar pulses from said timer/gate circuit and providing avideo signal corresponding thereto; and a video display for receivingthe video signal from said video processor and displaying thepredetermined area within the patient.
 16. Apparatus according to claim11, further comprising movement means for producing relative movementbetween said antenna and the patient, and wherein said receiver receivesa plurality of sets of reflected radar pulses, and wherein saidtimer/gate circuit selects radar pulses from among each set, theselected pulses corresponding to a predetermined volume within thepatient.
 17. A radar tomography apparatus, comprising:an antenna foremitting a plurality of radar pulses toward an adjacent patient, and forreceiving a plurality of reflected radar pulses reflected from subdermalfeatures within the patient; a matrix filter, disposed between saidantenna and the patient, for filtering the emitted and reflected radarpulses; a duplexer for switching said antenna between a transmit modeand a receiver mode; a transmitter for providing the radar pulses tosaid antenna; a receiver for receiving the reflected radar pulses fromsaid antenna; a timer/gate circuit for controlling said receiver tocause only radar pulses reflected from a predetermined area of interestwithin the patient to be received, the selected pulses including pulseswhich discriminate subdermal structure from contiguous subdermalstructure; and a processor for controlling said timer/gate circuit tocause said predetermined area to be scanned to different locationswithin the patient.
 18. Apparatus according to claim 17, furthercomprising display means for receiving the radar pulses corresponding tothe predetermined area from said receiver, and for displaying arepresentation of the predetermined area.
 19. Apparatus according toclaim 17, further comprising movement means for producing relativemovement between said antenna and the patient, and wherein saidtransmitter provides a plurality of sets of radar pulses to saidantenna, each set being emitted at a different position, and whereinsaid timer/gate circuit causes said receiver to receive only radarpulses reflected from a predetermined volume within the patient. 20.Apparatus according to claim 19, further comprising processor means for(1) receiving the radar pulses corresponding to the predetermined volumefrom said receiver, (2) converting these received radar pulses todigital signals, (3) storing the digital signals, and (4) processing thestored digital signals to provide an output signal corresponding to arepresentation of the predetermined volume.
 21. A radar tomographymethod, comprising the steps of:emitting a plurality of radar pulsestoward a patient, using an antenna adjacent the patient; providing theplurality of radar pulses to said antenna; receiving a plurality ofreflected radar pulses which correspond to the emitted plurality ofradar pulses reflected from subdermal features within the patient; andselecting predetermined radar pulses from among the received radarpulses, the selected radar pulses corresponding to a predetermined areaof interest within the patient, the selected pulses including pulseswhich discriminate subdermal structure from contiguous subdermalstructure.
 22. A method according to claim 21, further comprising thestep of displaying a representation of the predetermined area within thepatient based on the selected radar pulses.
 23. A method according toclaim 22, wherein said display step comprises the steps of:convertingthe selected radar pulses into a video signal; and receiving the videosignal and displaying the representation of the predetermined area ofthe patient.
 24. A method according to claim 23, further comprising thesteps of:converting the video signal into a digital signal; receivingthe digital signal, processing the digital signal, and providing anoutput digital signal which corresponds to the predetermined area withinthe patient; and converting the output digital signal into an analogsignal for display on a video display.
 25. A method according to claim24, further comprising the steps of:receiving the output digital signal;storing the output digital signal, and providing a plurality of storeddigital signals to cause a plurality of predetermined areas within thepatient to be displayed.
 26. A method according to claim 21, furthercomprising the steps of filtering the emitted radar pulses and thereflected radar pulses with a matrix filter.
 27. A method according toclaim 21, wherein said emitting step includes the steps of:controllingan aperture of said antenna; and further comprising the step of:switching said antenna from a receive mode to a transmit mode.
 28. Amethod according to claim 27, further including the steps of filteringthe emitted radar pulses and the reflected radar pulses with a matrixfilter.
 29. A method according to claim 21, wherein said transmittingstep comprises the steps of:generating a plurality of generated radarpulses; modulating the generated radar pulses to produce the pluralityof radar pulses provided to said antenna; and controlling the modulatingstep to produce the plurality of radar pulses at predetermined timings.30. A method according to claim 29, further comprising the step ofconverting the selected radar pulses into a video signal; andwhereinsaid controlling step synchronizes said modulating step and saidconverting step.
 31. A radar tomography method, comprising the stepsof:emitting a plurality of radar pulses toward a patient, and receivinga plurality of reflected radar pulses reflected from subdermal featureswithin the patient, using an antenna adjacent the patient; guiding theemitted and reflected pulses toward and from the patient, respectively,using a matrix filter; providing the plurality of radar pulses to saidantenna; receiving the plurality of reflected radar pulses from saidantenna, using a receiver; selecting predetermined ones of the reflectedradar pulses received by said receiver, the selected radar pulsescorresponding to a predetermined area of interest within the patient,the selected pulses including pulses which discriminate subdermalstructure from contiguous subdermal structure; and displaying arepresentation of the predetermined area within the patient, based onthe selected radar pulses.
 32. A method according to claim 31, furthercomprising the step of controlling an aperture of said antenna.
 33. Amethod according to claim 32, further comprising the step ofsynchronizing said aperture control step, said emitting step, saidselecting step, and said displaying step.
 34. Apparatus according toclaim 31, further comprising the step of producing relative movementbetween said antenna and the patient, and wherein said receiving stepincludes the step of receiving a plurality of sets of reflected radarpulses, and wherein said selecting step includes the step of selectingradar pulses from among each set, the selected pulses corresponding to apredetermined volume within the patient.
 35. A radar tomography method,comprising the steps of:emitting a plurality of radar pulses toward apatient, and receiving a plurality of reflected radar pulses reflectedfrom subdermal features within the patient, using an antenna adjacentthe patient; filtering the emitted and reflected radar pulses; switchingsaid antenna between a transmit mode and a receive mode; providing theradar pulses to said antenna; receiving the reflected radar pulses fromsaid antenna, using a receiver; controlling said receiver to cause onlyradar pulses reflected from a predetermined area within the patient tobe received, the selected pulses including pulses which discriminatesubdermal structure from contiguous subdermal structure; and causingsaid predetermined area to be scanned to different locations within thepatient.
 36. A method according to claim 35, further comprising the stepof displaying a representation of the predetermined area.
 37. A methodaccording to claim 36, further comprising the step of producing relativemovement between said antenna and the patient, and wherein said emittingstep emits a plurality of sets of radar pulses, each set being emittedat a different position, and wherein said controlling step causes saidreceiver to receive only radar pulses reflected from a predeterminedvolume within the patient.
 38. A method according to claim 37, furthercomprising a processing step for (1) receiving the radar pulsescorresponding to the predetermined volume from said receiver, (2)converting these received radar pulses to digital signals, (3) storingthe digital signals, and (4) processing the stored digital signals toprovide an output signal corresponding to a representation of thepredetermined volume.